The present invention relates to a reclining angle adjustment device for adjusting the angle of inclination of the seat back of a reclining seat, i.e., the reclining angle of the reclining seat.
Japanese Patent Publication No. 57-11207 discloses a reclining angle adjustment device having a pawl and a rack engageable and disengageable for roughly adjusting the reclining angle of a reclining seat, and a planetary gear mechanism for fine adjustment of the reclining angle. Another reclining angle adjustment device disclosed in Japanese Laid-Open Utility Model Publication No. 56-80739 includes a balancing spiral spring added to the device shown in the aforesaid reclining angle adjustment device.
The latter reclining angle adjustment device comprises an intermediate gear plate having an outer gear, an upper arm having an inner gear meshing with the outer gear of the intermediate gear plate, an angularly movable shaft on which the intermediate gear plate and the upper arm are angularly movably mounted respectively at concentric and eccentric portions of the shaft, a lower shaft supporting the angularly movable shaft, a release lever for unlocking the intermediate gear plate from the lower arm for rough adjustment of the reclining angle, a control handle for turning the angularly movable shaft for fine adjustment of the reclining angle, a grooved pin fixed to the lower arm through a pin bracket, and a spiral spring having an inner end engaging in the groove of the pin for imposing a turning force produced at the outer end thereof on the intermediate gear plate.
The spiral spring and the intermediate gear plate are coaxially disposed, but are substantially spaced axially from each other. In order to transmit the turning force produced at the outer end of the spiral spring to the intermediate gear plate, the intermediate gear plate has a projecting outer edge portion with its distal end bent toward the outer end of the spiral spring, the outer end of which engages the bent distal end of the intermediate gear plate. Therefore, the point where the outer end of the spiral spring engages the bent distal end of the intermediate gear plate, i.e., the point where the motion is transmitted to the intermediate gear plate, and the plane in which the intermediate gear plate is turned, are spaced from each other by a large distance (hereinafter referred to as an "offset"). When the intermediate gear plate is tilted with respect to the angularly movable shaft, a large torque is produced to generate large frictional forces between the angularly movable shaft and other surrounding components such as the intermediate gear plate. Therefore, the conventional reclining angle adjustment device has been disadvantageous in that a large force is required to turn the angularly movable shaft, i.e., the force required to operate the control handle should be large.